There is a prior art for producing an electric power from wave power wherein the art comprises a first structure fixed or moored to the bottom of the water, a second structure capable of moving with a wave and making a relative motion to the first structure, and putting a piezoelectric film between the first structure and the second structure for generating an electric power by the tension and slack, and thereby converting the relative motion of the first structure and the second structure into the electric power. (Japanese patent No. 3377590)